The present invention relates generally to a method and apparatus for making a friction plate having a friction material facing and to the friction material itself. More specifically, the invention is directed to a method and apparatus for making a friction plate having a unitary, or single, circumferentially edge wound friction material on one or both sides of a core plate.
The present invention also relates generally to automatic transmission clutch plates, and more particularly, to a clutch plate having a friction material bonded thereto where the friction material is blanked as a straight notched strip of friction material. The friction material is formed into a circular shape and is bonded to the core plate.
The present invention relates to a method and apparatus for making friction materials for use with a wet-type multi-plate clutch and further relates to the friction material itself. The prior art multi-plate clutches generally comprise a plurality of interleaved clutch discs and reaction plates which engage to provide the transmission of energy from a drive engine to a drive wheel. Wet-type clutches also utilize a lubricant such as oil to reduce clutch wear, cool the friction facings of the clutch discs and provide desired hydrostatic forces between the clutch plates and clutch discs.
The friction material is usually composed of fibrous paper which normally is impregnated with a phenolic resin. The friction material is commonly cut from a continuous strip of rectangular sheeting composed of the friction material which is fed through the die or cutting apparatus. The friction material is relatively expensive and, therefore, it is desirable to optimize the elimination of waste from the manufacturing process.
Once the friction material is impregnated with the phenolic thermoset resin, it cannot be economically recycled. Further, elimination of waste product from the manufacture process assists in meeting compliance standards. The proper disposal of any scrap is the focus of increasing regulation by current environmental regulators. Any scrap resulting from the cutting process must be disposed of in an appropriate manner and, because of the materials from which the friction facing is manufactured, this disposal is becoming increasingly costly.
Further, in the interest of optimizing clutch life, operational smoothness, and cooling efficiency for the friction facings, the literature and art relating to wet-type clutches provides numerous clutch designs producing a large variety of friction facing materials and designs of friction facing materials. A common friction facing, currently available is shown by the disclosure of U.S. Pat. Nos. 4,260,047 and 4,674,616 which disclose friction discs, for use with clutches, which are formed from friction material and produced from the joining of a plurality of separate arcuate segments. The arcuate segments are pre-grooved to allow cooling oil to flow over the friction facing during clutch operation.
The U.S. Pat. Nos. 5,094,331, 5,460,255, 5,571,372, 5,776,288, 5,897,737 and 6,019,205 disclose clutch friction plates having a large number of individually placed friction material segments on the plate. The segments are in a spaced apart relationship such that an oil groove is provided between every adjacent segment.
The U.S. Pat. Nos. 3,871,934 and 4,002,225 show a friction material wound around the outer periphery disc, such that it overlaps the disc on both sides. The overlap is then cut at intervals around the periphery and folded onto the surface of the disc.
The U.S. Pat. No. 5,335,765, discloses a friction member having sets of first grooves and second grooves disposed in a radial plane and inclined obliquely backwardly in relation to the direction of rotation.
The U.S. Pat. Nos. 5,615,758 and 5,998,311 show friction yarn facing materials with no grooves, but rather, the warp and fill yarns form channels to allow for the flow of fluid therethrough.
The manufacturing of many of these friction materials produce a large amount of unused or scrap material. It is, therefore, a primary object of the invention to effectively reduce the amount of scrap remaining after cutting of the friction material.
It is also desired that the sufficient cooling and lubrication of the friction material and clutch plates occurs such that smooth engagement and disengagement of the clutch is maintained without creating excessive wear on the members of the clutch and friction facing material. Many prior art friction material designs incorporate the use of grooves or slot patterns within the facing material to achieve the desired cooling and lubrication by allowing the passage of a fluid such as oil through the friction facings. Such cooling grooves are generally produced from one of three labor intensive methods. One method provides that the friction material is pre-grooved prior to being cut and applied to the clutch plate in a manner such as that taught by U.S. Pat. No. 4,260,047. Another method of producing grooves utilizes configured tooling to compress portions of the friction material during the hot pressure bonding process. The third method involves producing cut grooves in a finished friction plate by mounting the plate onto a fixture and passing multiple milling and grinding wheels through the friction material to cut distinct grooves of desired depth and definition.
The common failing of the previous designs of friction materials lies in the formation of intricate shapes and designs which consequently leads to manufacturing complexities, increased tooling costs, increased scrap production and the resultant concerns regarding proper disposal of the scrap. Further, the previous friction materials are all individually manufactured to specific types of friction clutches and, generally speaking, cannot be used in a wide variety of applications.
It is an object of the present invention to manufacture a friction clutch plate having distinct cooling groove patterns of desired depth and definition without the need for secondary operations and attendant machinery.
It is another object of the invention to provide an apparatus for making a continuous friction material which nearly scrapless in its manufacture.
It is yet another object of the present invention to provide a method and apparatus for making a friction material having a plurality of desired grooves therein.
Yet another object of the invention is to provide a method and apparatus for making a friction material having design advantages designated to produce enhanced product performance, and specifically reduced drag and improved shift feel (i.e., the ratio of end point coefficient of friction/midpoint coefficient of friction).
Yet a further object of the invention is to produce a method and apparatus for making a friction material having the capability of maintaining static pressure and holding dynamic fluid flow within the grooves of the friction material during operation of the engaged clutch disc and clutch plate.
It is another object of the invention to provide a friction material which is universally applicable to differing types of clutch usage.
Yet another object of the invention is to provide a method for bonding the friction material to a core plate by induction bonding, or other suitable methods, of the friction material to the core plate.
A unitary, circumferentially edge wound friction material and a method and apparatus for making a wet-type friction clutch plate are disclosed. The friction material has a plurality of A-notches and is a unitary, or continuous strip of material. The friction material is oriented on the clutch plate so as to create desired lubrication and cooling pumping functions through full depth oil channels created in the friction material. The orientation of the notches in the friction material achieves a desired direction of oil flow radially into or out of the clutch plate and also creates a desired amount of hydrostatic pressure. The size of the friction material and the shape, spacing and orientation of the notches all operate to control the degree of fluid pumping, the hydrostatic pressure, and the amount of cooling of the friction clutch plate.
In particular, the present invention describes a method and apparatus for making a clutch plate with an unitary, circumferentially edge wound friction material. The friction material is blanked with a desired number of notches as a straight strip of material and then is wound circumferentially to cover a face of the core plate. The notches allow the strip to be edge wound around an outer circumference of the core plate and also to produce desired grooves in the completed clutch plate.
In a preferred aspect, the notches have a generally xcex9-shape where each notch has an apex which compensates for tear and compression of the friction material when the friction material is circumferentially placed on the core plate. In a preferred aspect, the apex has a generally circular shape which prevents the friction material from fracturing or separating. The unique geometry of the xcex9-notch and its apex promotes both desirable tension and desirable compression in the friction material.
The notched friction material provides a significant improvement (greater than 50%) (i.e., from 18-32% with full ring to 80-90% with notch friction material depending on geometry) in friction material utilization over conventional full ring blanked friction facings. In certain embodiments, the notches are xe2x80x9cdead endxe2x80x9d such that there is no groove exit at the outside diameter of the friction plate. These xe2x80x9cdead endxe2x80x9d grooves retain the fluid at the friction interface. This is especially desirable in low fluid flow application, (where it is difficult to obtain high fluid flow).
In another embodiment, the a portion of the apex of the notches is removed, preferably by being sanded, or chamfered, such that there is restricted fluid flow from one end of the groove to the other end of the groove. These restricted flow groove exits provide a reduction in parasitic drag when the clutch is not applied.
One criterion in determining the shape, spacing and orientation of the notches in the friction material of this invention is the ratio of the circumference (360xc2x0) to the desired number of grooves in the length of friction material to be placed on the core plate. That is, 360xc2x0÷number of grooves=angle of each xcex9-notch.
As the performance requirements for automobiles become more stringent, the clutches must be able to provide high torque at high RPMs thereby operating efficiently at high temperatures. This performance requirement therefore demands more expensive, higher performance materials for use as the friction material. Thus, as the material costs increase, the present invention provides for an efficient method to produce a friction plate which minimizes the friction surface area while simultaneously striving to maintain cooling and lubrication requirements. The xcex9-notched friction material is responsive to the greater heat generation and the heat dissipation within the clutch which are necessary to meet the performance standards for the higher RPM/smaller engines common to today""s automobile.
Another important performance requirement of today""s automotive clutches is to produce minimal drag when the clutch is not applied, e.g. an open reverse clutch that is rotating but not applied when cruising at highway speed. Lower open clutch pack drag translates into higher fuel efficiency of the vehicle. The present invention produces lower open pack (parasitic) drag than other conventional designs (non-groove, cut grooved, molded groove).
In the method of making the clutch plate of the present invention, a strip of friction material is blanked out, or notched, with the desired xcex9-notch geometry defining each notch. The blanked out strip of friction material is cut to a desired length. The length of xcex9-notched friction material is picked up by a loading device, and is circumferentially placed adjacent a bonding nest. The bonding nest is used to help assemble the components of the clutch plate: the xcex9-notched friction material and a core plate. The loading device comprises a plurality of connected links where each link has at least one vacuum port. The linked loading device is moved adjacent the cut strip of friction material. The vacuum is engaged which allows the loading device to pick up the cut strip of friction material. The links of the linked loading device are moved, or laterally rotated, to form a closed circle. The linked loading device is positioned in coaxially alignment with the nest. The vacuum is released and the friction material is placed in the nest.
A core plate is placed in the nest and the above described process is repeated to place a second strip of friction material on top of the core plate.
Thereafter, the friction material is adhered to the core plate in a desired manner. The method for adhering the core plate involves using a thermosetting adhesive coating on the core plate. Thereafter, the friction material and core plate are compressed and heated in a suitable manner. The core plates can be stacked into a multiple nesting arrangement and heated in an oven. In another method, the assembled core plate with the friction materials adjacent thereto can be heated by conduction. Yet another method involves heating the core plate and friction materials adjacent thereto for with an induction coil.
The various embodiments of the present invention will be more readily understood, in their application to the objectives of this invention by reference to the accompanying drawings and the following description of the preferred embodiments of the invention.